The existing method for venous blood oxygenation monitored is either through an invasive fiber optic catheter, or intermittently by blood sampling and CO-oximetry. However, catheterization can be costly and can include inherent risks. Therefore, due to the inherent risks of catheterization, venous oximetry is limited only to those critically ill patients. The clinical application of venous oximetry is numerous, including severe sepsis and septic shock, severe trauma and hemorrhagic shock, and heart failure and cardiac arrest.